Hard gold-based plating solution

ABSTRACT

To provide a hard gold-based plating solution which enables selective partial plating treatment and is suitable for electronic components such as a connector. A hard gold-based plating solution of the present invention comprises: a soluble gold salt or a gold complex; a conductive salt; and a chelating agent, wherein the hard gold-based plating solution further comprises an aromatic compound having one or more nitro groups, for example, an aromatic compound selected from the group consisting of nitrobenzoic acid, dinitrobenzoic acid and nitrobenzene sulfonic acid. The hard gold-based plating solution further comprises at least one metal salt of a cobalt salt, a nickel salt and a silver salt, or polyethyleneimine as an organic additive.

TECHNICAL FIELD

The present invention relates to a hard gold-based plating treatmenttechnology. In particular, the present invention relates to a hardgold-based plating solution which is suitable in forming contactmaterials of electronic components such as a connector and applies hardgold plating and hard gold alloy plating. The hard gold-based plating ofthe present application refers to either hard gold plating or hard goldalloy plating. A plating solution for applying the hard gold-basedplating is referred to as a hard gold-based plating solution.

BACKGROUND ART

Conventionally, gold plating has been used for electronic devices andelectronic components for reasons of excellent electrical properties andcorrosion resistance or the like of gold, and has been widely used foran application of protecting a surface of a connecting terminal of theelectronic component or the like. The gold plating is used as surfacetreatment of electronic components such as an electrode terminal of asemiconductor device, a lead formed on a resin film and a connectorconnecting the electronic device.

In the electronic components such as the connector connecting theelectronic device, the gold plating is used as the surface treatment.Since corrosion resistance, abrasion resistance and electricalconductivity are required as the properties of the electroniccomponents, the hard gold-based plating is often used. For example, hardgold alloy platings such as gold-cobalt-based alloy plating andgold-nickel-based alloy plating have been known as the hard gold-basedplating through the ages (Patent Documents 1 and 2).

Copper or a copper alloy is generally used as a material for theelectronic components such as the connector. Nickel plating isordinarily applied on the surface of the copper or the copper alloy inthe case of applying the hard gold-based plating, and the hardgold-based plating is then applied on the surface of the nickel plating.

When the hard gold-based plating is applied to the electronic componentssuch as the connector, partial plating treatment is required so that thehard gold-based plating is applied to only a necessary portion. That is,the hard gold-based plating is applied to only the necessary portion,and the ungeneration of the deposition of the hard gold-based plating onan unnecessary portion is required. The reason is that when the hardgold-based plating is applied to the unnecessary portion of theconnector, a solder also infiltrates the unnecessary portion to reduceelectric properties in soldering treatment for electric connection.Another reason is that unless the hard gold-based plating is depositedon the unnecessary portion, the used amount of gold can be suppressed toenable the reduce amount of gold. To meet such a demand, a technologycapable of selectively performing hard gold-based plating treatment ononly a necessary portion is proposed (for example, Patent Document 3).

A gold-cobalt alloy plating solution of the conventional technique isused to deposit a gold alloy plating film on only a desired place of theelectronic components such as the connector and to suppress thedeposition of the gold alloy plating film on the unnecessary place.Thereby, hard gold-based plating can be applied.

PRIOR ART DOCUMENTS Patent Document

-   Patent Document 1: DE Patent 1111987-   Patent Document 2: JP Patent Application Laid-Open No. Sho 60-155696-   Patent Document 3: JP Patent Application Laid-Open No. 2008-45194

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Incidentally, since gold or gold alloy plating has excellent materialproperties, the gold or gold alloy plating is very often applied to aportion requiring electric connection in the current electroniccomponents. A hard gold-based plating solution selectively enablingpartial plating treatment is required for various object parts. However,the types of hard gold-based plating solutions are fewer. That is, inthis situation, there is need for a novel hard gold-based platingsolution enabling selective partial plating treatment as proposed inPatent Document 3.

The present invention was developed in the light of the above-describedsituations. It is an object of the present invention to provide a hardgold-based plating solution which enables selective partial platingtreatment and is suitable for electronic components such as a connector.

A hard gold-based plating solution of the present invention comprises: asoluble gold salt or a gold complex; a conductive salt; and a chelatingagent, wherein the hard gold-based plating solution further comprises anaromatic compound having one or more nitro groups. When the hardgold-based plating solution comprising the soluble gold salt or the goldcomplex, the conductive salt, and the chelating agent further comprisesthe aromatic compound having one or more nitro groups, the selectivepartial plating treatment is enabled by hard gold-based plating.

Preferably, the hard gold-based plating solution further comprises atleast one metal salt selected from a cobalt salt, a nickel salt and asilver salt. The metal salt can convert a plating film into a gold alloyto harden the film.

The hard gold-based plating solution may comprise polyethyleneimine asan organic additive in place of the metal salts such as the cobalt salt,the nickel salt and the silver salt. The polyethyleneimines havingvarious molecular weights can be used, regardless of structures such asa straight chain structure and a branch structure. The addition of theorganic additive can harden the plating film as well as the addition ofthe metal salt.

In the hard gold-based plating solution, the soluble gold salt or thegold complex can be used as a gold ion source. Specifically, there canbe used gold(I) potassium cyanide, gold(II) potassium cyanide, goldammonium cyanide, gold(I) potassium chloride, gold(II) potassiumchloride, gold(I) sodium chloride, gold(II) sodium chloride, goldpotassium thiosulfate, gold sodium thiosulfate, gold potassium sulfite,gold sodium sulfite or any combination of two or more thereof. Gold(I)potassium cyanide is particularly preferable.

The gold concentration of the hard gold-based plating solution isdesirably in the range of 1 g/L to 20 g/L in terms of gold. The goldconcentration of less than 1 g/L complicates treatment of the hardgold-based plating solution at a high current density, with the resultthat this tends to complicate high-speed plating treatment. This isbecause the gold concentration exceeding 20 g/L increases a drag-outloss of gold from the plating solution (A slight plating solution isattached to a connector or the like as an object to be plated, to bebrought out to the next process. For example, even if several drops ofthe plating solution are brought out, weight loss of the gold from theplating solution is increased as the gold concentration is higher.),causing an increase in manufacturing cost. A gold salt concentration ismore preferably 2 g/L to 16 g/L in terms of gold.

When the hard gold-based plating solution according to the presentinvention comprises the cobalt salt, a soluble cobalt compound can beused as a cobalt source. For example, cobalt sulfate, cobalt chloride,cobalt carbonate, cobalt sulfamate, cobalt gluconate and a combinationof two or more thereof can be used. Preferably, the cobalt compound isan inorganic cobalt salt, and particularly cobalt sulfate.

The concentration of the cobalt salt in the plating solution isdesirably in the range of 0.05 g/L to 10 g/L in terms of cobalt. Theconcentration of less than 0.05 g/L reduces the amount of cobaltco-deposited in the plating film, with the result that this tends not toimprove the hardening of the hard gold-based plating. The concentrationexceeding 10 g/L tends to reduce the stability of the plating solution.More preferably, the concentration of the cobalt salt is 0.1 g/L to 3g/L in terms of cobalt.

When the hard gold-based plating solution according to the presentinvention comprises the nickel salt, a soluble nickel compound can beused as a nickel source. For example, nickel sulfate, nickel chloride,nickel carbonate, nickel sulfamate, nickel gluconate and a combinationof two or more thereof can be used. The nickel compound is particularlypreferably nickel sulfate.

The concentration of the nickel salt in the plating solution isdesirably in the range of 0.05 g/L to 30 g/L in terms of nickel. Theconcentration of less than 0.05 g/L reduces the eutectoid amount ofnickel in the plating film, with the result that this tends to unimprovethe hardening of the hard gold-based plating. The concentrationexceeding 30 g/L tends to reduce the stability of the plating solution.More preferably, the nickel concentration is 0.1 g/L to 20 g/L in termsof nickel.

When the hard gold-based plating solution comprises the silver salt, asoluble silver compound can be used as a silver source. For example,silver cyanide and a salt thereof, silver chloride, silver carbonate,silver nitrate and a combination of two or more thereof can be used. Thesilver compound is particularly preferably silver cyanide.

The concentration of the silver salt in the plating solution isdesirably in the range of 0.05 g/L to 100 g/L in terms of silver. Theconcentration of less than 0.05 g/L reduces the eutectoid amount ofsilver in the plating film, with the result that this tends to unimprovethe hardening of the hard gold-based plating. The concentrationexceeding 100 g/L tends to reduce the stability of the plating solution.More preferably, the silver concentration is 0.1 g/L to 50 g/L in termsof silver.

When the hard gold-based plating solution comprises polyethyleneimine asthe organic additive, the concentration of the organic additive in theplating solution is preferably 0.1 g/L to 300 g/L. The concentration ofless than 0.1 g/L tends to unimprove the hardening of the hardgold-based plating. The concentration exceeding 300 g/L tends to reducethe stability of the plating solution. More preferably, theconcentration is 1 g/L to 200 g/L.

Both an organic compound and an inorganic compound can be used as theconductive salt in the hard gold-based plating solution. Examples of theorganic compound include a compound containing carboxylic acids such ascitric acid, tartaric acid, adipic acid, malic acid, succinic acid,lactic acid and benzoic acid and salts thereof, and a phosphonate groupand a salt thereof. Examples of the inorganic compound include alkalimetal salts or ammonium salts of phosphoric acid, sulfurous acid,nitrous acid, nitric acid and sulfuric acid or the like, alkali cyanidesand ammonium cyanide. The combination of two or more thereof can be alsoused.

The concentration of the conductive salt in the plating solution isdesirably in the range of 0.1 g/L to 300 g/L. More preferably, theconcentration is 1 g/L to 200 g/L.

A carboxyl group-containing compound and a phosphonate group-containingcompound or the like can be used as the chelating agent in the hardgold-based plating solution. Examples of the carboxyl group-containingcompound include citric acid, potassium citrate, sodium citrate,tartaric acid, oxalic acid and succinic acid. The phosphonategroup-containing compound has a phosphonate group or a salt thereof in amolecule. Examples of the phosphonate group-containing compound includecompounds having a plurality of phosphonate groups in a molecule such asaminotrimethylenephosphonic acid, 1-hydroxyethylidene-1,1-diphosphonicacid, ethylenediamine tetramethylene phosphonic acid anddiethylenetriamine pentamethylenephosphonic acid, and alkali metal saltsor ammonium salts thereof. A nitrogen compound as an auxiliary chelatingagent can be also used with the carboxyl group-containing compound.Examples of the nitrogen compound include ammonia, ethylene diamine andtriethanolamine. The combination of two or more of the chelating agentscan be also used.

The concentration of the chelating agent in the plating solution isdesirably in the range of 0.1 g/L to 300 g/L. The concentration of lessthan 0.1 g/L tends to hinder a chelating action. The concentrationexceeding 300 g/L tends to cause undissolution of the chelating agent inthe plating solution. More preferably, the concentration is 1 g/L to 200g/L.

Dinitrobenzoic acid, nitrobenzoic acid and nitrobenzene sulfonic acidcan be used as the aromatic compound having one or more nitro groups inthe hard gold-based plating solution. The addition of the aromaticcompounds into the plating solution enables the selective partialplating treatment to effectively suppress the deposition of the hardgold-based plating on an unnecessary portion.

The concentration of the aromatic compound having one or more nitrogroups in the plating solution is desirably in the range of 0.01 g/L to30 g/L. The concentration of less than 0.01 g/L easily causes thedeposition of the gold alloy plating on the unnecessary portion. Theconcentration exceeding 30 g/L excessively suppresses the platingdeposition amount wholly, with the result that this tends to complicatethe hard gold-based plating on a necessary portion. More preferably, theconcentration is 0.05 g/L to 15 g/L.

The hard gold-based plating solution can comprise a pH adjuster and abuffering agent or the like in addition to the basic compositiondescribed above. Alkali metal hydroxides such as potassium citrate andpotassium hydroxide, or acid materials such as citric acid andphosphoric acid can be used as the pH adjuster. Citric acid, tartaricacid, oxalic acid, succinic acid, phosphoric acid, sulfurous acid orsalts thereof or the like can be used as the buffering agent.

As the plating treatment condition, the pH of the hard gold-basedplating solution is preferably set to 3 or more. The plating treatmentshould preferably be performed at a solution temperature of 5° C. to 90°C. The pH of less than 3 tends to easily cause generation of cyanogengas. More preferably, the plating treatment should be performed underthe plating treatment condition that pH is 4 or more and a solutiontemperature is 20° C. to 70° C. The applicable range of a currentdensity in the plating treatment is wide. The optimal current densityvalue can be selected according to conditions such as an object to beplated, a plating device and a flow rate of the plating solution. Thehard gold-based plating solution according to the present invention canparticularly correspond to the plating treatment condition of the highcurrent density such as high-speed plating treatment.

Advantageous Effects of the Invention

The hard gold-based plating treatment can be performed on only thenecessary portion of the electronic components such as the connector byusing the hard gold-based plating solution according to the presentinvention. Particularly, when the hard gold-based plating treatment isperformed on a surface of nickel plating as an under layer, partialplating treatment can be selectively performed.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described.

First Embodiment

The embodiment describes results of inspecting plating properties of ahard gold-based plating solution of a gold-cobalt alloy.

Example 1

In Example 1, results of performing a Hull cell test usingdinitrobenzoic acid as an aromatic compound having one or more nitrogroups to inspect electrodeposition properties thereof will bedescribed. A composition of a hard gold-based plating solution was asfollows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)cobalt sulfate: 3.6 g/L (0.76 g/L in terms of cobalt)citric acid: 150 g/Lpotassium hydroxide: 20 g/Ldinitrobenzoic acid: 1 g/L, 5 g/LpH: 4.4solution temperature: 60° C.

In the Hull cell test, a commercially available Hull cell tester(manufactured by Yamamoto-MS Co., Ltd.) was used. A Hull cell plate madeof brass (length: 70 mm, width: 100 mm, thickness: 0.3 mm) having bothsurfaces on which nickel plating (thickness: 10 μm) was applied was usedas a base material to be plated. Plating treatment time was set to 30seconds and a current to be energized was set to 3 A. A plating solutionwas strongly agitated during plating treatment.

Hull cell evaluation was performed by measuring plating film thicknessesof nine places of the plated Hull cell plate. The nine places of theHull cell plate were selected at a predetermined interval in the widthdirection of the Hull cell plate in a horizontal direction at a portion(a portion dipped in the plating solution) located at the upper side byabout 2 cm from the bottom of the Hull cell plate contacting theinternal bottom face of the Hull cell tester.

The plating film thicknesses were measured with the fluorescent X-rayfilm thickness meter (manufactured by SII NanoTechnology Inc.). As anapproximate current density value in each of the nine points (No. 1 to9) at which the film thicknesses were measured, No. 1 was 0.3 A/dm²; No.2, 1 A/dm²; No. 3, 2 A/dm²; No. 4, 3 A/dm²; No. 5, 4 A/dm²; No. 6, 5.5A/dm²; No. 7, 7.5 A/dm²; No. 8, 10 A/dm²; and No. 9, 13.5 A/dm². ThisHull cell evaluation was performed on both the surface of the platedHull cell plate and the rear face thereof. Results of measuring the filmthicknesses of the points are shown in Table 1. The current densityvalues of the nine places described above represent current densities onthe surface side of the Hull cell plate. The current density values onthe back side of the Hull cell plate are unknown. The current densityvalues on the rear face side of the Hull cell plate are much lower thanthose on the surface side.

TABLE 1 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0040.000 0.064 0.000 0.000 2 0.170 0.020 0.000 0.013 0.001 0.001 3 0.3390.060 0.000 0.009 0.006 0.000 4 0.474 0.126 0.003 0.007 0.004 0.000 50.692 0.253 0.005 0.007 0.000 0.003 6 0.846 0.406 0.002 0.003 0.0000.001 7 1.036 0.628 0.006 0.007 0.000 0.004 8 1.148 0.894 0.016 0.0100.006 0.003 9 1.137 1.038 0.198 0.007 0.003 0.001 (Film thickness: μm)

Results of a hard gold-based plating solution to which dinitrobenzoicacid is not added are also shown for comparison in Table 1. Numbers 1 to9 shown in Table 1 represent measurement points at the nine places ofthe Hull cell plate. The results of columns of hyphens are the resultsof the hard gold-based plating solution to which dinitrobenzoic acid isnot added. Each of the columns of 1 g/L, and 5 g/L represents theresults of the hard gold-based plating solution containingdinitrobenzoic acid of each concentration of 1 g/L and 5 g/L (The sameapplies to Tables of measurement results of the film thicknesses of Hullcell plates to be shown later.). As is apparent from the measurementresults of the film thicknesses of the surface of the Hull cell plate,it became clear that when dinitrobenzoic acid is added, the plating filmthickness of a low current density side is rapidly decreased. It alsobecame clear that when the added amount thereof is set to 5 g/L, theplating of the low current density side is further suppressed.Furthermore, in the case of the hard gold-based plating solution towhich dinitrobenzoic acid was not added, hard gold-based plating wasalso applied on the rear face side of the Hull cell plate. However, itfurther became clear that when dinitrobenzoic acid is added, the rearface side is virtually free from any plating treatment.

Example 2

In Example 2, nitrobenzoic acid was used as an aromatic compound havingone or more nitro groups. A composition of a hard gold-based platingsolution of Example 2 is the same as that of Example 1. The compositionof Example 2 is different from that of Example 1 only in a point thatnitrobenzoic acid is used in place of dinitrobenzoic acid of Example 1.A Hull cell test condition and evaluation thereof were also the same asthose of Example 1. Results of measuring film thicknesses of pointsaccording to Example 2 are shown in Table 2.

TABLE 2 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0120.000 0.064 0.001 0.000 2 0.170 0.044 0.001 0.013 0.003 0.000 3 0.3390.109 0.006 0.009 0.001 0.000 4 0.474 0.224 0.005 0.007 0.003 0.003 50.692 0.405 0.019 0.007 0.004 0.000 6 0.846 0.577 0.043 0.003 0.0020.000 7 1.036 0.778 0.113 0.007 0.000 0.000 8 1.148 1.032 0.385 0.0100.003 0.000 9 1.137 1.091 0.874 0.007 0.001 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 2, it became clear thatwhen nitrobenzoic acid is added, the plating film thickness of a lowcurrent density side is rapidly decreased. It also became clear thatwhen the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzoic acid is added unlike the case of the hard gold-basedplating solution to which nitrobenzoic acid is not added, a rear faceside of a Hull cell plate is virtually free from any plating treatment.

Example 3

In Example 3, nitrobenzene sulfonic acid was used as an aromaticcompound having one or more nitro groups. A composition of a hardgold-based plating solution of Example 3 is the same as that of Example1 except that the former uses nitrobenzene sulfonic acid in place ofdinitrobenzoic acid of Example 1. A Hull cell test condition andevaluation thereof were also same as those of Example 1. Results ofmeasuring film thicknesses of points according to Example 3 are shown inTable 3.

TABLE 3 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0200.007 0.064 0.018 0.002 2 0.170 0.068 0.004 0.013 0.010 0.000 3 0.3390.153 0.009 0.009 0.007 0.007 4 0.474 0.266 0.018 0.007 0.003 0.000 50.692 0.449 0.026 0.007 0.007 0.002 6 0.846 0.646 0.053 0.003 0.0020.000 7 1.036 0.844 0.140 0.007 0.000 0.003 8 1.148 1.047 0.446 0.0100.000 0.003 9 1.137 1.106 0.912 0.007 0.003 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 3, it became clear thatwhen nitrobenzene sulfonic acid is added, the plating film thickness ofa low current density side is rapidly decreased. It also became clearthat when the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzene sulfonic acid is added unlike the case of the hardgold-based plating solution to which nitrobenzene sulfonic acid is notadded, a rear face side of a Hull cell plate is virtually free from anyplating treatment.

Example 4

Example 4 describes results of performing a high-speed partial platingtest using dinitrobenzoic acid as an aromatic compound having one ormore nitro groups to inspect electrodeposition properties thereof. Acomposition of a hard gold-based plating solution of a gold-cobalt alloywas as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)cobalt sulfate: 3.6 g/L (0.76 g/L in terms of cobalt)citric acid: 150 g/Lpotassium hydroxide: 20 g/Ldinitrobenzoic acid: 0.5 g/L, 1.0 g/L, 1.5 g/L, 2.0 g/L, 3.0 g/L, 5.0g/LpH: 4.4solution temperature: 60° C.

In the high-speed partial plating test, a Ni-plated (thickness of 10 μm)brass plate as an object to be plated was used. In order to confirm thedeposition selectivity of a gold plating film, the brass plate wasfluid-tightly sealed by a silicon packing so that a circular portionhaving a diameter of 9 mm was in an exposed state. However, a groove(width: 2 mm, length: 20 mm, depth: 3 mm) extending from one end of theexposed circular portion was formed between nickel plating and a siliconpacking mask. When the plating solution is jetted to the exposedcircular portion which is not masked with the silicon packing, platingis formed on the circular portion. The plating solution passes through agap formed in the groove portion, and is discharged from the end side ofthe groove portion. Since the mask exists on the upper part of thegroove portion, the groove portion has a current density lower than thatof the circular exposed portion on which no mask exists, at the time ofelectrolysis. Therefore, when this high-speed partial plating deviceperforms plating treatment, it is ideal to perform plating treatment ononly the circular portion and to perform no plating treatment on thegroove portion.

As the plating treatment condition, a flow rate was controlled to 15L/min and a current density was controlled to 50 A/dm² to form agold-cobalt alloy plating film having a thickness of 0.5 μm.

A plating state in the case of changing the concentration ofdinitrobenzoic acid in the plating solution was externally observed. Itbecame clear that as the added amount of dinitrobenzoic acid isincreased, the groove portion is free from any plating treatment.

Then, plating film thicknesses were measured at four places of thegroove portion of each of test samples plated at concentrations toinspect an average plating film thickness. The results are shown inTable 4. The plating film thicknesses were measured by a fluorescentX-ray film thickness meter (manufactured by SII NanoTechnology Inc.).

TABLE 4 Concentration (g/L) 0 0.5 1.0 1.5 2.0 3.0 5.0 Average film 0.0590.022 0.011 0.003 0.002 0.001 0.001 thickness (μm)

From the results of Table 4, it became clear that when the concentrationof dinitrobenzoic acid in the plating solution is increased, platingtreatment proceeds selectively on a circular plating portion of asubstrate, and the groove portion that does not require any platingtreatment is free from any plating treatment.

Second Embodiment

The embodiment describes results of inspecting plating properties of ahard gold-based plating solution of a gold-nickel alloy.

Example 5

In Example 5, dinitrobenzoic acid was used as an aromatic compoundhaving one or more nitro groups. A composition of a hard gold-basedplating solution was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)nickel sulfate: 9 g/L (2 g/L in terms of nickel)citric acid: 150 g/Lpotassium hydroxide: 20 g/Ldinitrobenzoic acid: 1 g/L, 5 g/LpH: 4.4solution temperature: 60° C.

A Hull cell test condition and evaluation were same as those ofExample 1. Results of measuring film thicknesses of points according toExample 5 are shown in Table 5.

TABLE 5 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0050.003 0.046 0.011 0.000 2 0.170 0.014 0.003 0.009 0.002 0.000 3 0.3290.049 0.004 0.014 0.000 0.000 4 0.497 0.106 0.001 0.008 0.004 0.001 50.731 0.253 0.004 0.013 0.001 0.000 6 0.923 0.465 0.006 0.011 0.0040.001 7 1.052 0.716 0.001 0.009 0.003 0.003 8 1.028 0.904 0.018 0.0150.004 0.000 9 0.986 0.856 0.219 0.011 0.000 0.000 (Film thickness: μm)

Results of a hard gold-based plating solution to which dinitrobenzoicacid is not added are also shown for comparison in Table 5. As isapparent from the results shown in Table 5, it became clear that whennitrobenzoic acid is added as in the case of the first embodiment, theplating film thickness of a low current density side is rapidlydecreased. It also became clear that when the added amount thereof isset to 5 g/L, plating of the low current density side is furthersuppressed. In the case of the hard gold-based plating solution to whichdinitrobenzoic acid is not added, hard gold-based plating is alsoapplied to a rear face side of a Hull cell plate. However, it furtherbecame clear that when dinitrobenzoic acid is added, the rear face sideis virtually free from any plating treatment.

Example 6

In Example 6, nitrobenzoic acid was used as an aromatic compound havingone or more nitro groups. A composition of a hard gold-based platingsolution of Example 6 is the same as that of Example 5. The compositionof Example 6 is different from that of Example 5 only in a point thatnitrobenzoic acid is used in place of dinitrobenzoic acid of Example 5.A Hull cell test condition and evaluation thereof were same as those ofExample 1. Results of measuring film thicknesses of points according toExample 6 are shown in Table 6.

TABLE 6 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0120.006 0.046 0.009 0.005 2 0.170 0.032 0.000 0.009 0.007 0.004 3 0.3290.096 0.000 0.014 0.003 0.003 4 0.497 0.184 0.006 0.008 0.000 0.002 50.731 0.384 0.003 0.013 0.000 0.002 6 0.923 0.574 0.008 0.011 0.0030.002 7 1.052 0.786 0.026 0.009 0.002 0.001 8 1.028 0.901 0.126 0.0150.002 0.000 9 0.986 1.060 0.708 0.011 0.001 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 6, it became clear thatwhen nitrobenzoic acid is added, the plating film thickness of a lowcurrent density side is rapidly decreased. It also became clear thatwhen the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzoic acid is added unlike the case of the hard gold-basedplating solution to which nitrobenzoic acid is not added, a rear faceside of a Hull cell plate is virtually free from any plating treatment.

Example 7

In Example 7, nitrobenzene sulfonic acid was used as an aromaticcompound having one or more nitro groups. A composition of a hardgold-based plating solution of Example 7 is the same as that of Example5. The composition of Example 7 is different from that of Example 5 onlyin a point that nitrobenzene sulfonic acid is used in place ofdinitrobenzoic acid of Example 5. A Hull cell test condition andevaluation thereof were also same as those of Example 1. Results ofmeasuring film thicknesses of points according to Example 7 are shown inTable 7.

TABLE 7 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.084 0.0220.004 0.046 0.015 0.000 2 0.170 0.063 0.005 0.009 0.005 0.002 3 0.3290.172 0.008 0.014 0.001 0.000 4 0.497 0.322 0.008 0.008 0.000 0.001 50.731 0.562 0.016 0.013 0.006 0.002 6 0.923 0.800 0.042 0.011 0.0030.000 7 1.052 0.967 0.133 0.009 0.002 0.002 8 1.028 1.069 0.477 0.0150.000 0.002 9 0.986 1.086 0.954 0.011 0.004 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 7, it became clear thatwhen nitrobenzene sulfonic acid is added, the plating film thickness ofa low current density side is rapidly decreased. It also became clearthat when the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzoic sulfonic acid is added unlike the case of the hardgold-based plating solution to which nitrobenzene sulfonic acid is notadded, a rear face side of a Hull cell plate is virtually free from anyplating treatment.

Example 8

In Example 8, as in Example 4 described above, results of performing ahigh-speed partial plating test using dinitrobenzoic acid as an aromaticcompound having one or more nitro groups to inspect electrodepositionproperties thereof will be described. A composition of a hard gold-basedplating solution of a gold-nickel alloy was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)nickel sulfate: 9 g/L (2 g/L in terms of nickel)citric acid: 150 g/Lpotassium hydroxide: 20 g/Ldinitrobenzoic acid: 0.5 g/L, 1.0 g/L, 1.5 g/L, 2.0 g/L, 3.0 g/L, 5.0g/LpH: 4.4solution temperature: 60° C.

A test sample, a device and a plating condition or the like of thehigh-speed partial plating test were the same as those of Example 4.

Also in Example 8, a plating state in the case of changing theconcentration of dinitrobenzoic acid in the plating solution wasexternally observed. It became clear that as the added amount ofdinitrobenzoic acid is increased, a groove portion is free from anyplating treatment.

In Example 8, results of inspecting average plating film thicknesses ofthe groove portion as in Example 4 described above are shown in Table 8.The film thicknesses were also inspected as in Example 4.

TABLE 8 Concentration (g/L) 0 0.5 1.0 1.5 2.0 3.0 5.0 Average film 0.0420.024 0.012 0.003 0.003 0.001 0.001 thickness (μm)

From the results of Table 8, as in Example 4, it became clear that whenthe concentration of dinitrobenzoic acid in the plating solution isincreased, plating treatment proceeds selectively on a circular platingportion of a substrate, and no plating treatment is performed on thegroove portion that does not require any plating treatment is free fromany plating treatment.

Third Embodiment

In the embodiment, results of inspecting plating properties of a hardgold-based plating solution of a gold-silver alloy will be described.

Example 9

In Example 9, dinitrobenzoic acid was used as an aromatic compoundhaving one or more nitro groups. A composition of a hard gold-basedplating solution was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)silver cyanide: 10 g/L (8 g/L in terms of silver)potassium cyanide: 50 g/Ldinitrobenzoic acid: 1 g/L, 5 g/LpH: 12solution temperature: 20° C.

A Hull cell test condition and evaluation were the same as those ofExample 1. Results of measuring film thicknesses of points according toExample 9 are shown in Table 9.

TABLE 9 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.212 0.1100.001 0.159 0.079 0.001 2 0.246 0.144 0.000 0.057 0.001 0.001 3 0.3010.174 0.011 0.016 0.000 0.000 4 0.331 0.190 0.019 0.010 0.002 0.001 50.385 0.259 0.054 0.008 0.001 0.000 6 0.397 0.333 0.220 0.007 0.0000.000 7 0.371 0.335 0.292 0.006 0.002 0.001 8 0.382 0.369 0.311 0.0110.000 0.000 9 0.339 0.354 0.333 0.023 0.002 0.000 (Film thickness: μm)

Results of a hard gold-based plating solution to which dinitrobenzoicacid is not added are also shown for comparison in Table 9. As isapparent from the results shown in Table 9, it became clear that whennitrobenzoic acid is added as in the case of the first embodiment, theplating film thickness of a low current density side is rapidlydecreased. It also became clear that when the added amount thereof isset to 5 g/L, plating of the low current density side is furthersuppressed. It further became clear that when dinitrobenzoic acid isadded unlike the case of the hard gold-based plating solution to whichdinitrobenzoic acid is not added, a rear face side of a Hull cell plateis virtually free from any plating treatment.

Example 10

In Example 10, nitrobenzoic acid was used as an aromatic compound havingone or more nitro groups. A composition of a hard gold-based platingsolution of Example 10 is the same as that of Example 9. The compositionof Example 10 is different from that of Example 9 only in a point thatnitrobenzoic acid is used in place of dinitrobenzoic acid of Example 10.A Hull cell test condition and evaluation thereof were the same as thoseof Example 1. Results of measuring film thicknesses of points in Example10 are shown in Table 10.

TABLE 10 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.212 0.1460.001 0.159 0.082 0.002 2 0.246 0.192 0.000 0.057 0.002 0.001 3 0.3010.232 0.015 0.016 0.001 0.004 4 0.331 0.253 0.067 0.010 0.000 0.001 50.385 0.308 0.201 0.008 0.002 0.003 6 0.397 0.332 0.254 0.007 0.0010.000 7 0.371 0.364 0.294 0.006 0.003 0.000 8 0.382 0.349 0.302 0.0110.000 0.001 9 0.339 0.332 0.309 0.023 0.000 0.003 (Film thickness: μm)

As is apparent from the results shown in Table 10, it became clear thatwhen nitrobenzoic acid is added, the plating film thickness of a lowcurrent density side is rapidly decreased. It also became clear thatwhen the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzoic acid is added unlike the case of the hard gold-basedplating solution to which nitrobenzoic acid is not added, a rear faceside of a Hull cell plate is virtually free from any plating treatment.

Example 11

In Example 11, nitrobenzene sulfonic acid was used as an aromaticcompound having one or more nitro groups. A composition of a hardgold-based plating solution of Example 11 is the same as that of Example9. The composition of Example 11 is different from that of Example 9only in a point that nitrobenzene sulfonic acid is used in place ofdinitrobenzoic acid of Example 9. A Hull cell test condition andevaluation thereof were also the same as those of Example 1. Results ofmeasuring film thicknesses of points in Example 11 are shown in Table11.

TABLE 11 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.212 0.1830.001 0.159 0.132 0.002 2 0.246 0.240 0.000 0.057 0.002 0.001 3 0.3010.290 0.019 0.016 0.006 0.003 4 0.331 0.316 0.178 0.010 0.003 0.001 50.385 0.320 0.307 0.008 0.002 0.004 6 0.397 0.331 0.367 0.007 0.0060.005 7 0.371 0.312 0.338 0.006 0.004 0.007 8 0.382 0.335 0.328 0.0110.000 0.001 9 0.339 0.355 0.354 0.023 0.004 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 11, it became clear thatwhen nitrobenzene sulfonic acid is added, the plating film thickness ofa low current density side is rapidly decreased. It also became clearthat when the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzene sulfonic acid is added unlike the case of the hardgold-based plating solution to which nitrobenzene sulfonic acid is notadded, a rear face side of a Hull cell plate is virtually free from anyplating treatment.

Example 12

In Example 12, as in Example 4, results of performing a high-speedpartial plating test using dinitrobenzoic acid as an aromatic compoundhaving one or more nitro groups to inspect electrodeposition propertiesthereof will be described. A composition of a hard gold-based platingsolution of a gold-silver alloy was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)silver cyanide: 10 g/L (8 g/L in terms of silver)potassium cyanide: 50 g/Ldinitrobenzoic acid: 0.5 g/L, 1.0 g/L, 1.5 g/L, 2.0 g/L, 3.0 g/L, 5.0g/LpH: 12solution temperature: 20° C.

A test sample, a device and a plating treatment condition or the like ofthe high-speed partial plating test were the same as those of Example 4.

Also in Example 12, a plating state in the case of changing theconcentration of dinitrobenzoic acid in the plating solution wasexternally observed. It became clear that as the added amount ofdinitrobenzoic acid is increased, a groove portion is free from anyplating treatment.

In Example 12, results of inspecting average plating film thicknesses ofthe groove portion as in Example 4 are shown in Table 12. The filmthicknesses were also inspected as in Example 4.

TABLE 12 Concentration (g/L) 0 0.5 1.0 1.5 2.0 3.0 5.0 Average film0.059 0.048 0.015 0.004 0.003 0.002 0.001 thickness (μm)

From the results of Table 12, as in Example 4, it became clear that whenthe concentration of dinitrobenzoic acid in the plating solution isincreased, plating treatment proceeds selectively on a circular platingportion of a substrate, and the groove portion that does not require anyplating treatment is free from any plating treatment.

Fourth Embodiment

In the embodiment, results of inspecting plating properties of a hardgold-based plating solution of only gold will be described. Polyethyleneamine was used as an organic additive contributing to hardening.

Example 13

In Example 13, dinitrobenzoic acid was used as an aromatic compoundhaving one or more nitro groups. A composition of a hard gold-basedplating solution of only gold was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)polyethylene amine: 10 g/Lcitric acid: 150 g/Ldinitrobenzoic acid: 1 g/L, 5 g/LpH: 7solution temperature: 65° C.

A Hull cell test condition and evaluation were the same as those ofExample 1. Results of measuring film thicknesses of points according toExample 13 are shown in Table 13.

TABLE 13 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.196 0.0600.002 0.106 0.023 0.000 2 0.308 0.150 0.006 0.029 0.003 0.000 3 0.4350.245 0.017 0.014 0.002 0.000 4 0.560 0.381 0.019 0.013 0.000 0.001 50.638 0.469 0.034 0.010 0.000 0.000 6 0.707 0.537 0.048 0.011 0.0010.000 7 0.721 0.640 0.108 0.009 0.001 0.002 8 0.840 0.750 0.302 0.0080.000 0.000 9 0.905 0.850 0.596 0.017 0.000 0.000 (Film thickness: μm)

Results of a hard gold-based plating solution to which dinitrobenzoicacid is not added are also shown for comparison in Table 13. As isapparent from the results shown in Table 13, it became clear that whennitrobenzoic acid is added as in the case of the first embodiment, theplating film thickness of a low current density side is rapidlydecreased. It also became clear that when the added amount thereof isset to 5 g/L, plating of the low current density side is furthersuppressed. It further became clear that when dinitrobenzoic acid isadded unlike the case of the hard gold-based plating solution to whichdinitrobenzoic acid is not added, a rear face side of a Hull cell plateis virtually free from any plating treatment.

Example 14

In Example 14, nitrobenzoic acid was used as an aromatic compound havingone or more nitro groups. A composition of a hard gold-based platingsolution of Example 14 is the same as that of Example 13. Thecomposition of Example 14 is different from that of Example 13 only in apoint that nitrobenzoic acid is used in place of dinitrobenzoic acid ofExample 13. A Hull cell test condition and evaluation thereof were thesame as those of Example 1. Results of measuring film thicknesses ofpoints in Example 13 are shown in Table 14.

TABLE 14 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.196 0.0680.002 0.106 0.031 0.002 2 0.308 0.168 0.006 0.029 0.002 0.000 3 0.4350.275 0.019 0.014 0.002 0.000 4 0.560 0.428 0.031 0.013 0.000 0.000 50.638 0.527 0.054 0.010 0.000 0.001 6 0.707 0.604 0.128 0.011 0.0020.002 7 0.721 0.650 0.249 0.009 0.000 0.000 8 0.840 0.750 0.488 0.0080.000 0.000 9 0.905 0.829 0.671 0.017 0.001 0.002 (Film thickness: μm)

As is apparent from the results shown in Table 14, it became clear thatwhen nitrobenzoic acid is added, the plating film thickness of a lowcurrent density side is rapidly decreased. It also became clear thatwhen the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzoic acid is added unlike the case of the hard gold-basedplating solution to which nitrobenzoic acid is not added, a rear faceside of a Hull cell plate is virtually free from any plating treatment.

Example 15

In Example 15, nitrobenzene sulfonic acid was used as an aromaticcompound having one or more nitro groups. A composition of a hardgold-based plating solution of Example 15 is the same as that of Example13. The composition of Example 15 is different from that of Example 13only in a point that nitrobenzene sulfonic acid is used in place ofdinitrobenzoic acid of Example 9. A Hull cell test condition andevaluation thereof were also the same as those of Example 1. Results ofmeasuring film thicknesses of points in Example 15 are shown in Table15.

TABLE 15 Surface Rear face — 1 g/L 5 g/L — 1 g/L 5 g/L 1 0.196 0.0750.002 0.106 0.039 0.000 2 0.308 0.187 0.007 0.029 0.005 0.000 3 0.4350.306 0.021 0.014 0.002 0.000 4 0.560 0.476 0.034 0.013 0.000 0.004 50.638 0.586 0.079 0.010 0.000 0.003 6 0.707 0.671 0.174 0.011 0.0020.003 7 0.721 0.683 0.333 0.009 0.005 0.009 8 0.840 0.769 0.542 0.0080.000 0.002 9 0.905 0.865 0.745 0.017 0.000 0.000 (Film thickness: μm)

As is apparent from the results shown in Table 15, it became clear thatwhen nitrobenzene sulfonic acid is added, the plating film thickness ofa low current density side is rapidly decreased. It also became clearthat when the added amount thereof is set to 5 g/L, plating of the lowcurrent density side is further suppressed. It further became clear thatwhen nitrobenzene sulfonic acid is added unlike the case of the hardgold-based plating solution to which nitrobenzene sulfonic acid is notadded, a rear face side of a Hull cell plate is virtually free from anyplating treatment.

Example 16

In Example 16, as in Example 4, results of performing a high-speedpartial plating test using dinitrobenzoic acid as an aromatic compoundhaving one or more nitro groups to inspect electrodeposition propertiesthereof will be described. A composition of a hard gold-based platingsolution was as follows.

gold(I) potassium cyanide: 12 g/L (8 g/L in terms of gold)polyethylene amine: 10 g/Lcitric acid: 150 g/Ldinitrobenzoic acid: 0.5 g/L, 1.0 g/L, 1.5 g/L, 2.0 g/L, 3.0 g/L, 5.0g/LpH: 7solution temperature: 65° C.

A test sample, a device and a plating treatment condition or the like ofthe high-speed partial plating test were the same as those of Example 4.

Also in Example 16, a plating state in the case of changing theconcentration of dinitrobenzoic acid in the plating solution wasexternally observed. It became clear that as the added amount ofdinitrobenzoic acid is increased, a groove portion is free from anyplating treatment.

In Example 16, results of inspecting average plating film thicknesses ofthe groove portion as in Example 4 are shown in Table 16. The filmthicknesses were also inspected as in Example 4.

TABLE 16 Concentration (g/L) 0 0.5 1.0 1.5 2.0 3.0 5.0 Average film0.051 0.034 0.013 0.003 0.002 0.002 0.001 thickness (μm)

From the results of Table 16, as in Example 4, it became clear that whenthe concentration of dinitrobenzoic acid in the plating solution isincreased, plating treatment proceeds selectively on a circular platingportion of a substrate, and the groove portion that does not require anyplating treatment is free from any plating treatment.

INDUSTRIAL APPLICABILITY

The present invention can apply the hard gold-based plating treatment toonly the necessary portion of the electronic components such as theconnector. Particularly, when the hard gold-based plating is applied onthe surface of the nickel plating applied on the under layer, thepartial plating treatment can be selectively applied.

1. A hard gold-based plating solution comprising: a soluble gold salt ora gold complex; a conductive salt; and a chelating agent, wherein thehard gold-based plating solution further comprises an aromatic compoundhaving one or more nitro groups.
 2. The hard gold-based plating solutionaccording to claim 1, wherein the hard gold-based plating solutionfurther comprises at least one metal salt of a cobalt salt, a nickelsalt and a silver salt.
 3. The hard gold-based plating solutionaccording to claim 1, wherein the hard gold-based plating solutionfurther comprises polyethyleneimine as an organic additive.
 4. The hardgold-based plating solution according to claim 1, wherein the aromaticcompound is selected from nitrobenzoic acid, dinitrobenzoic acid andnitrobenzene sulfonic acid.
 5. The hard gold-based plating solutionaccording to claim 2, wherein the aromatic compound is selected fromnitrobenzoic acid, dinitrobenzoic acid and nitrobenzene sulfonic acid.6. The hard gold-based plating solution according to claim 3, whereinthe aromatic compound is selected from nitrobenzoic acid, dinitrobenzoicacid and nitrobenzene sulfonic acid.